The present invention relates to a photosensitive paste capable of curing upon irradiation of light, and a substrate for plasma display panel (hereinafter referred to as xe2x80x9cPDPxe2x80x9d) having a rib formed by using the paste.
It is expected that PDP is used in a thin type large screen display device. In general, PDP is provided with a substrate. A typical substrate for PDP comprises a pair of glass flat plates and a rib (also referred to as a barrier rib or a barrier) having a predetermined size, said glass flat plates facing each other at a distance through said rib. With such a construction, the rib forms a plurality of discharge display cells capable of partitioning a space between a pair of glass flat plates, thereby making it possible to contain a discharge gas such as neon, helium or xenon.
Various methods of producing the rib have been suggested. For example, Japanese Unexamined Patent Publication (Kokai) No. 9-265905 discloses a transfer method comprising the steps of curing a pasty mixture of a glass or ceramic powder, a binder containing an organic additive, and an organosilicate compound by means of heating or irradiation of light to produce a molded article and then calcining the molded article to produce a rib. However, the organic additive contained in the binder of the pasty mixture is liable to inhibit it from absorbing light to rapidly produce a molded article by means of curing caused by light. When the glass flat plate provided with the rib made of such a mixture has a large area, it is liable to make it difficult to perform a heat control in case of curing and calcination with heating. As a result, the temperature distribution becomes non-uniform and, therefore, it is liable to become impossible to impart a predetermined quality to the rib. In case of calcination, the organic additive contained in the binder is burned off and it becomes substantially unnecessary for the rib in the final form.
The pasty mixture used for producing the rib is also disclosed in the publication other than the above publication. For example, Japanese Unexamined Patent Publication (Kokai) No. 8-50811 discloses a photosensitive glass insulating paste comprising a glass powder mainly containing bismuth oxide and zinc oxide, and an acrylic copolymer as a binder. However, when the molded article made by using this paste is calcined to obtain a rib, if the binder is burned off in the same manner as that described above, the glass powder is simultaneously molten to transfer to the burned off portion. As a result, the rib has a volume smaller than that of the molded article by about 20%, accompanying shrinkage of the molded article.
Since the above glass powder mainly contains bismuth oxide and zinc oxide and has low melting point, the glass powder is liable to flow even at comparatively low temperature. In case of calcination, such flow can cause deformation of the molded article and the rib may not have the predetermined shape. The non-uniformity of the shape of the rib not only exerts an influence on the shape of the discharge display cell to impart non-uniformity to the display, but can also lead to leakage of a discharge gas, resulting in reduction of a life of PDP.
Japanese Unexamined Patent Publication (Kokai) No. 8-119725 discloses a photosensitive paste comprising a low-softening point glass powder mainly containing lead oxide, and an alumina powder. As is generally used as a material for shielding radiation, lead has very high mass absorption coefficient. Accordingly, even if the photosensitive paste mainly containing lead is exposed to light, it is liable to take a very long time to cure by light absorption due to lead.